Silvacore Pro by Duraflue adjustable length: 5", 6", Silver, Black.This is an adjustable part and you will be supplied with extra internal insulation to fill the void created when you extend. Hide and strengthen the joint using an extra narrow locking band. This is a twin wall clip together chimney part used to build a new chimney. Twin wall clip together chimney can be as close as 5cm to combustible materials (7cm if passing through a sealed void). No glue or sealants required. When we say 5 or 6 we speak of